[mythtv-users] Bob deinterlace and Xv problems

[Doug Larrick]

Dan Seddon wrote:

> When I choose to use bob deinterlace without XvMC, meaning it must be 
> using Xv, everything starts off fine then after a short while X starts 
> to climb in it's processor usage until it's using all that remains after 
> myth (about %65). It took me a while to catch on to this (it causes 
> stuttering which after months of trying to get rid of XvMC I wasn't 
> looking in the right place), it was only when I logged in from my laptop 
> and did a top that I saw what was going in. Turning off bob-deinterlace 
> solves the problem - which is bad as you really need bob when displaying 
> on a montior as I am. I'm sure it's not a processing limitation as in 
> the worse case all that can be happening is that Xv is splitting the 
> fields and doubling up the frames on the fly, before scaling up? So, it 
> has four times the scaling to do - but that shouldn't be an issue to an 
> Nvidia card. Has anyone seen this and, even better, know how to prevent it?

Besides the processing you mention, bob also doubles the effective
output framerate, and so doubles the overhead of the video output thread.

If "Onefield" deinterlacing (which does the same processing but doesn't
double the framerate) causes similar issues the problem is elsewhere,
but if not I'd suspect you're on the hairy edge of required processor power.

Also make sure you're using a good video sync method (look at
'mythfrontend --verbose playback').  OpenGL vsync is good, so long as
your nVidia driver is not the (79xx? 81xx?) version that sucks down a
ton of CPU time if you turn that option on.

-Doug

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